1. Field of the Invention
The present invention relates to an edge lighted plate for use as an exit sign or for other purposes.
2. Description of the Prior Art
Many cities require buildings to have a standby source of power for lighted exit signs in the event that the conventional AC power fails. Rather than employing a generator and extra wiring for the signs, it it cheaper and more convenient to use batteries for each sign as the backup system. Most emergency exit signs use two 20 watt and two 7 watt incandescent light bulbs located in a box employing lenses which form the sign. The two 20 watt bulbs are powered by 110 volts AC to maintain these bulbs normally on. The two 7 watt bulbs are normally off. In the event that the AC power fails and the 20 watt bulbs go off, the two 7 watt bulbs are turned on. They are powered by 6 volts DC from three 2 volt batteries. A transformer is employed for reducing the 110 volts AC to 6 volts AC which is rectified and applied to the batteries for maintaining the batteries charged. Regulations require the batteries to be able to maintain the emergency bulbs on for 11/2 hours. Signs of this type have disadvantages in that in the event of an emergency, such as a fire, which causes the 20 watt bulbs to go off and the 7 watt bulbs to turn on, the amount of light produced by the 7 watt bulbs is at such a low level that in a smoke filled room, the sign cannot be seen. Moreover, the 20 watt bulbs burn a relatively large amount of energy and hence generate a large amount of heat in their confined space. This reduces their lifetime to a period of about 1 year requiring frequent replacement. In addition, the total package of these prior exit signs including their batteries is relatively large.